I have molds similar to this from Bebe, and I absolutely LOVE them, BUT... I'm kind of a stickler and want a completely rectangular bar. Mine don't bow _much_, but they do bow, and it's noticable if you look closely at the cut bars. If you don't care about that, this type of mold is awesome, though. You don't need to line/oil them, just make sure they're clean before you pour. Super simple to get the soap out too.
Anywho, if you want a perfectly rectangular bar check out Woodfields molds, or another wood mold with silicon lining. They're definitely pricey, but worth the investment in my opinion.